#include <iostream>
#include <limits.h>
#include <cmath>
#include <algorithm>
#include <vector>
#include <utility>
#include <fstream>
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

#define mp make_pair
#define pb push_back
#define ff first
#define ss second

int n,k=0,i,j,a[2000001];

int main()
{
   f>>n;
   for(i=2; i<=n; i++)
        if (a[i]==0)
            for(j=2*i; j<=n; j+=i)
                a[j]=1;

   for(i=2; i<=n; i++)
        if (a[i]==0) k+=1;

   g<<k<<endl;

   return 0;
}